Can anyone please explain this screenshot? (how do forts work?) EXPLAINED

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William Shakens

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So, that Austrian army is coming from Unterkarnten. How are they able to bypass my Star Fort in Alta Carinzia to attack me in Etschtal. How? I just realized I don't understand how forts work, troop-movement-wise, apparently.
1599178131787.png
 

Cancerofthehead

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If you want to learn about forts, look up the Reman’s Paradox Zone of Control YouTube video.

I believe would be an example of rule six, friendly zones of control, combined with zone of control not being exerted across borders.

Basically, if you want to cut an enemy in two with forts, you at least a two tile gap.
 
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Vince Whirlwind

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That fort will have hardly any effect on enemy movement.
No effect across national borders.
He can enter Gorizia from any neighbouring provice excecpt Friuli.
If he wants to enter Friuli he can do it from Trieste.
I think the logic you expect is reasonable in that particular situation.
 

William Shakens

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I understand the thing in the South, Vince Whirlwind, Goritzia, Trieste, Friuli, I'm ok with that.

What is incredibly counter-intuitive to say the least is that they can completely bypass Alta Carintzia from Unterkarnten with the Alps in the North and South, and reach my army two provinces to the West of my fort. Is it because they have a fort of their own in Unterkarnten or the one in Etschtal that I was besieging

EDIT: So after watching the video Cancerofthehead recommented. The suggestion was rule #6 which says: "Forts that you control AND are in your territory, have a friendly zone of control, additionally to their normal ZoC. You can ALWAYS MOVE INTO OF FROM a province with friendly ZoC. So their fort Unterkarnten is projecting a friendly ZoC on my fort province, while their fort that I was besieging in Etschtal projects a friendly ZoC on the province of Lienz, therefore allowing them to ignore my fort's hostile ZoC thanks to their forts' friendly ZoC.

Incredibly counter-intuitive. Probably baffling. But at least there is a clear rule about it.
 
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Tulduil

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[...]

EDIT: So after watching the video Cancerofthehead recommented. The suggestion was rule #6 which says: "Forts that you control AND are in your territory, have a friendly zone of control, additionally to their normal ZoC. You can ALWAYS MOVE INTO OF FROM a province with friendly ZoC. So their fort Unterkarnten is projecting a friendly ZoC on my fort province, while their fort that I was besieging in Etschtal projects a friendly ZoC on the province of Lienz, therefore allowing them to ignore my fort's hostile ZoC thanks to their forts' friendly ZoC.
[...]

Small correction: Friendly ZoC does not cross borders into enemy provinces (the same as hostile ZoC).
So Unterkärnten does NOT project a ZoC (neither hostile nor friendly) on Alta Carinzia and the move would still be possible without a fort in Unterkärnten (because "can always move to adjacent hostile fort when not on a hostile fort" (in some situations you can even move to adjacent hostile forts when on a hostile fort but that does not apply here).
Alta Carnizia -> Lienz is possible because of Eschtal's friendly ZoC, as you correctly noticed.

Unterkärnten's only effect would be the reverse move: Without a fort in Unterkärnten (and no forts in Steiermark, Graz and Krain) the movement Lienz- > Alta Carnizia -> Unterkärnten would not be possible.


How could the move have been prevented?
- Occupying Unterkärnten would not have a big effect, an army coming from Wienerwald -> Steiermark -> Alta Carnizia could still pass to Lienz/Eschtal
- Occupying Eschtal before(!!!) Austria's army started its move: Occupying Eschtal removes the frZoC from Lienz, making any move Alta Carnizia -> Lienz impossible.
As movement orders check for ZoCs only when given it can be possible that Austria bypasses Alta Carnizia even after Eschtal fell (as long as the movement was ordered when Eschtal was still under siege and therfore still projected frZoC on Lienz).
- Owning Lienz (important: "own" =/= "control"): If you owned Lienz (regardless of occupation status) any move Steiermark/Unterkärnten -> Alta Carnizia -> Lienz would be impossible because ZoCs never cross hostile borders and therefore Lienz isn't in Eschtal's frZoC.
However, owning Lienz only prevents movements from East to West, it does not block movements from West to East (Eschtal -> Lienz ("when not in hoZoC can always move to adjacent hoZoC"), Lienz -> Alta Carnizia ("when not on hostile fort can always move to adjacent hostile fort"), Alta Carnizia -> Unterkärnten/Steiermark ("can always move to frZoC")).



That said, this was an easy example for applying fort movement rules ingame. There are much more obscure examples.

Fort rules are complicated and sometimes interact with each other in unexpected (and sometimes unforseeable) ways but usually you can find an (at least theoretical) explanation why an AI move was possible after it happened. (And I said "theorectical" because there is no easy way to check an enemy army's Return Province which can often make big differences and also no easy way to check when and from where an AI movement order was issued)
 
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William Shakens

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Small correction:

Oh yeah it would make sense that they should have access to the fort to besiege it, you don't need a friendly ZoC for that. It's the crossing past it that's a head scratcher. I was indeed besieging Eschtal at positive 21% siege and I had a small unit because I was sure they couldn't get there from the East without taking Treviso or the Star Fort, or going North of The Alps.
 

Cancerofthehead

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One correction, he can move to Alta Carinzia regardless of the fort there as it is moving from a province with no zone of control. For example he could presumably still do that same movement if the fort was in Friuli instead.

As a general rule, I would assume that a single fort with enemy territory on either side can be crossed by your enemy unless there is something else blocking the movement. I learned this lesson from efforts to cut off the Ottomans at Sinai or Constantinople.